The present invention relates to a laser irradiation light detecting device, and particularly to a laser irradiation light detecting device having detecting means for receiving a reflected light pencil of a laser light pencil applied from a laser irradiating device provided with a non-linear optical medium for generating a second harmonic.
A device intended for use outdoors upon civil engineering construction and surveying work or the like, particularly, a device for providing the reference for a distance location has heretofore been in existence. A visible-light laser irradiating device has been used as this type of device. With technical advances in semiconductor laser emission, a semiconductor laser has been widely used in place of a laser using a gas such as a helium-neon gas or the like. In particular, a battery-operable laser irradiating device for applying red visible light has been used in general. Further, a device has come into being which modulates a laser light pencil, irradiates a target disposed at a distant location with it and detects its reflected light pencil to thereby control the irradiating direction of a laser beam.
However, the conventional visible-light laser irradiating device is accompanied by a problem that constraints and limitations are imposed on the output applied from the laser irradiating device from the viewpoint of the ability of the semiconductor laser and safety's sake and particularly when it is used at a bright location, it is hard to visually recognize red visible laser beam.
With the problem on its visibility in view, an attempt has been made to use the green greater in human relative visibility than the red. A solid green laser using a second harmonic has become a focus of attention. Although a visible-light laser irradiating device wherein this type of solid green laser has been incorporated into a laser oscillating device, has been developed, the solid green laser itself provides more power consumption and hence the visible-light laser irradiating device was unfit for battery driving.
The device which scans and detects a reflected laser light carries out a frequency modulation and a synchronism detection so as to distinguish from noise, however, for solid green laser direct modulation becomes hard at a modulation frequency, e.g., 100 KHz. Therefore, a serious problem arises in that the device must be constructed on a large scale when the device is used in combination with an externally-provided modulation device.